Printer with printhead and pressing body in point contact

ABSTRACT

A printer comprises a frame having a pair of side walls spaced apart a given distance according to a given width size of a recording medium. A platen is supported between the pair of side walls and has a surface for supporting the recording medium. A printhead, operable in a printing position thereof to perform a printing operation on the recording medium, is supported between the side walls for tilting movement and displacement in forward/backward and rightward/leftward directions. A pressing body is supported by the frame for pressing the printhead into contact with the surface of the platen. When the printhead is in the printing position, the printhead is freely pivotable to permit automatic angular adjustment thereof following the surface of the platen so that the printhead can contact the surface of the platen with a uniform surface pressure.

FIELD OF THE INVENTION

The present invention relates to a printer with a platen and aprinthead. More particularly, the present invention relates to a printerhaving a structure for supporting a printhead.

BACKGROUND ART

FIG. 7 shows an example of a conventional printer. The printer includesa platen 101 which is rotatably provided to bridge along the widthdirection of a recording medium (not shown). The printer also has aprinthead 102 which is disposed at the back of the platen 101. Further,the printer includes a pressing body 103 to press a front surface of theprinthead 102 from the rear thereof into contact with the platen 101.The pressing body 103 has a vertical shaft 104 and a horizontal shaft105. A torsion spring 106 is wound on the horizontal shaft 105 togenerate a pressing force. The vertical shaft 104 pierces the printhead102 to rotatably support the printhead 102.

FIGS. 8A and 8B show another example of a conventional printer. FIG. 8Arepresents a printhead 201 and FIG. 8(B) represents a frame 202. Asshown in the figure, the frame 202 has left and right side walls 203 and204 which are disposed facing each other at a distance depending on thewidth of a recording medium (not shown). The printhead 201 isincorporated between the left and right side walls 203 and 204. In thisexample, protrusions 205 and 206 are formed at both ends of the lowerportion of the printhead 201, respectively. Through holes 207 and 208are formed in the protrusions 205 and 206, respectively. On the otherside, in the lower portions of the left and right side walls 203 and204, through holes 209 and 210 are formed, respectively. In a statewhere the printhead 201 is incorporated in the frame 202, theabove-mentioned through holes 207, 208, 209, and 210 are aligned. Byinserting a shaft (not shown) in the through holes, the printhead 201can be provided to bridge rotatably with respect to the frame 202.

FIGS. 9A and 9B show still another example of a conventional printer. Apair of upper and lower pins 302 and 303 are formed at the left end inthe width direction of the printhead 301. In the same manner, a pair ofupper and lower pins 304 and 305 are formed at the right end in thewidth direction of the printhead 301. On the other hand, the frame 306has left and right side walls 307 and 308 which are disposed facing eachother at a distance depending on the width of a recording medium (notshown). A guide slit 309 is formed in the left side wall 307. The guideslit 309 branches into a vertical branch portion 310 and an arc-likebranch portion 311. In the same manner, a guide slit 312 is formed inthe right side wall 308. The guide slit 312 branches into a verticalbranch portion 313 and an arc-like branch portion 314. Theabove-mentioned printhead 301 is incorporated in the frame 306 dropwisefrom above. In an assembled state, the upper pin 302 is engaged with thearc-like branch portion 311 while the lower pin 303 is engaged with thevertical branch portion 310. In the same manner, the upper pin 304 isengaged with the arc-like branch portion 314 while the lower pin 305 isengaged with the vertical branch portion 313. In this state, theprinthead 301 rotates backward and forward with the lower pins 303 and305 being the center of the rotation. Here, the upper pins 302 and 304are guided by the arc-like branch portions 311 and 314, respectively.

In the conventional printer shown in FIG. 7, the printhead 102 isaxially supported by the vertical shaft 104 of the pressing body 103 sothat the printhead 102 can tilt right and left. Therefore, when thefront surface of the printhead 102 is pressed from the rear thereof intocontact with the platen 101 by the action of the torsion spring 106, theprinthead 102 can tilt and move right and left to absorb the deviation.However, since the horizontal shaft 105 connected with the verticalshaft 104 is fixedly supported with respect to the frame, the printhead102 cannot move backward and forward directions when pressed intocontact with the platen 101. Since the extent of the tilt of theprinthead 102 in the directions backward and forward can not beadjusted, it is difficult to completely absorb the dimensional error andthe installation error of the platen 101.

In the conventional printer shown in FIGS. 8A and 8B, the through holes207, 208, 209, and 210 must be aligned after the printhead 201 isincorporated in the frame 202. The positioning is time-consuming and,therefore, the fabrication is inferior. In addition, since the printhead201 and the frame 202 are coupled to each other by a horizontal shaft(not shown), the printhead 201 rotates only backward and forward. As theprinthead 201 can not tilt and move right and left, the deviation withthe platen (not shown) can not be absorbed. Still further, since thetilted position in the directions of backward and forward is regulated,the dimensional error and the installation error of the platen can notbe absorbed.

In the conventional printer shown in FIGS. 9A and 9B, the printhead 301can be incorporated in the frame 306 dropwise from the above, and thusfabrication is facilitated as compared with the conventional printershown in FIGS. 8A and 8B. However, this printer has a problem that,since the guide slits 309 and 312 having branches are formed in the leftand right side walls 307 and 308, the strength of the frame is lowered.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a printer having astructure in which a printhead is pressed uniformly in contact with aplaten. Another object of the present invention is to provide a printerwith excellent incorporativity of a printhead and excellent strength ofa frame.

A printer according to the present invention comprises a frame, aplaten, a printhead, and a pressing body as a basic structure. The framehas left and right side walls which are provided facing each other at adistance depending on the width of a recording medium. The platen isrotatably provided to bridge between the two side walls. The printheadis also provided between the two side walls, and is disposed at the backof the platen. The pressing body is incorporated in the frame to press afront surface of the printhead from the rear thereof into contact withthe platen By this construction, the printhead can tilt and displace inforward/backward and rightward/leftward directions according to theposition of the platen, and the pressing body is in point contact withthe printhead. With such a structure, during a printing operation, theprinthead can be pressed into contact with the platen so that it followsthe rotation of the platen.

Specifically, the printhead and the pressing body are formed of separatecomponents which can be separately incorporated. One of the printheadand the pressing body has a convex spherical surface portion, and theother has a plane portion. The convex spherical surface portion and theplane portion are in point contact with each other. Alternatively, theprinthead and the pressing body may have convex cylindrical surfaceportions which intersect each other to be made in point contact witheach other. Preferably, the printhead has a wide upper portion which ismade by pressing in contact with the platen and a narrow lower portionwhich is integral with the wide upper portion. On the other hand, theleft and right side walls have thin portions to be engaged wish the wideupper portion and thick portions to be en gaged with the narrow lowerportion, respectively.

According to the present invention, a printhead can tilt and movebackward and forward and right and left according to the position of aplaten. Further, a pressing body is in point contact with a printhead.Since the operating portion of the press is a point, a printhead cantilt and move backward and forward and right and left, and can be madeby pressing uniformly in contact with a platen. By this construction,deviation can be prevented, which is effective for improving the printquality (by preventing a blur) and the linearity of advance of arecording medium. Further, since a pressing body and a printhead areindependent of each other, the printhead can be incorporated orexchanged with ease. Still further, a printhead is T-shaped having awide upper portion and a narrow lower portion integral with the wideupper portion. According to this, the side walls of a frame are dividedinto thin portions and thick portions. With such a structure, thestrength of the frame is improved. Further, a printhead can beincorporated in the frame dropwise from above, and the dead space insidethe frame can be effectively utilized. Different from the conventionalprinter, since there is no need to insert a horizontal shaft and theincorporation can be done from above, the fabrication is improved. Sincethrough holes through which a horizontal shaft is inserted are notnecessary, the structure of a die for forming a printhead can besimplified (sliding is unnecessary) to lower the cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are schematic drawings showing basic structures of a printeraccording to the present invention.

FIGS. 2A-2B are also schematic drawings showing a basic structure of aprinter according to the present invention.

FIGS. 3A and 3B are a plan view and a right elevational view,respectively, showing a specific structure of a printer according to thepresent invention.

FIGS. 4A and 4B are a plan view and an elevational view, respectively,showing the main portion of the printer shown in FIG. 3.

FIGS. 5A and 5B are a plan view and an elevational view, respectively,showing an example of a variation of the structure shown in FIG. 4.

FIGS. 6A and 6B are also a plan view and an elevational view,respectively, showing another example of a variation of the structureshown in FIG. 4.

FIG. 7 is a schematic drawing showing an example of a conventionalprinter.

FIGS. 8A-8B are schematic drawings showing another example of aconventional printer.

FIGS. 9A-9B are schematic drawings showing still another example of aconventional printer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail in the following with reference to the drawings. FIG. 1 showsbasic structures of a printer according to the present invention, andthree different aspects are denoted as (A), (B), and (C). A printershown in FIG. 1(A) includes a frame (not shown), a platen 1, a printhead2, and a pressing body 3 as a basic structure. The frame has left andright side walls which are disposed facing each other at a distancedepending on the width of a recording medium (not shown). The platen 1is rotatably provided to bridge between the two side walls.Specifically, the platen 1 comprises a cylindrical elastic body 4 madeof rubber or the like and a rotating shaft 5 which pierces the center ofthe elastic body 4. Both ends of the rotating shaft 5 are supported bythe left and right side walls of the frame. The printhead 2 is alsoprovided to bridge between the two side walls of the frame, and isdisposed at the back of the platen 1. Specifically, the printhead 2comprises a head-supporting body 6 on which a thermal element (notshown) is mounted and a pair of support members or pins 7 located atboth ends of the head-supporting body 6. The head-supporting body 6 andthe pins 7 can be integrally formed using a material such as aluminum.The pressing body 3 is incorporated in the frame to press a frontsurface of the printhead 2 into contact with the platen 1 from a rearsurface thereof. Specifically, the pressing body 3 has a horizontalshaft 8, a torsion spring 9 wound on the horizontal shaft 8, and a planemember 10 attached in the middle of the horizontal shaft 8. The torsionspring 9 generates pressing force to press forward the printhead 2 viathe plane member 10. By this construction, the thermal element, etc.provided on the printhead 2 is placed in contact with the platen 1.

As characteristic matters of the present invention, the printhead 2 isflexibly engaged with the two side walls of the frame via the pins 7 atits both ends, and can tilt and move backward and forward and right andleft according to the position of the platen 1. On the other hand, thepressing body 3 is in point contact with the printhead 2. With such astructure, during a printing operation, the printhead 2 can be presseduniformly into contact with the cylindrical body 4 following up therotation of the platen 1. It should be noted that the printhead 2 andthe pressing body 3 are formed of separate components which can beseparately incorporated. In the present embodiment, while the pressingbody 3 has a plane member 10, at the back of the head-supporting body 6,a convex spherical surface portion 11 is formed. The structure is suchthat the plane member 10 and the convex spherical surface portion 11 arein point contact with each other.

The printer shown in FIG. 1(B) has basically the same structure. Likereference numerals designate corresponding parts to those in the printershown in FIG. 1(A) so as to be understood easily. In the presentembodiment, the head-supporting body 6 has in the middle of its rearsurface a vertical convex cylindrical surface portion 11a. On the otherhand, the pressing body 3 comprises a torsion spring 9 shown by a thickline. The middle portion 10a of the torsion spring 9 extends in thehorizontal direction and has a convex cylindrical surface portion. Thevertical convex cylindrical surface portion 11a formed on the rearsurface of the head-supporting body 6 and the convex cylindrical surfaceportion formed on the horizontal middle portion 10a on the side of thepressing body 3 intersect each other to be kept in point contact witheach other.

The printer shown in FIG. 1(C) also has basically the same structure.Like reference numerals designate corresponding parts to those in theprinter shown in FIG. 1 (A) so as to be understood easily. At the rearsurface of the head-supporting body 6, a convex cylindrical surfaceportion 11b which extends in the horizontal direction is formed. On theother hand, the pressing body 3 has a vertical post 10b substantially inthe middle of the horizontal shaft 8. The vertical convex cylindricalsurface of the post 10b and the horizontal cylindrical surface portion11b on the side of the head-supporting body 6 intersect each other toform point contact between the bodies.

FIGS. 2A and 2B show another example of a structure of a printeraccording to the present invention. FIG. 2(A) shows the printhead 2 andFIG. 2(B) shows a frame 12. The printhead 2 has the head-supporting body6. A pair of upper and lower pins 7a and 7b are formed at the right endof the head-supporting body 6. In the same manner, a pair of upper andlower pins 7a and 7b are also formed at the left end of thehead-supporting body 6. The head-supporting body 6 and the pins 7a and7b can be integrally formed using a material such as aluminum. Differentfrom a conventional printer, there is no need to provide through holesthrough which a horizontal shaft is inserted, and thus, the structure ofa die for forming the head-supporting body 6 can be simplified (slidingis unnecessary) to lower the cost. As shown in the figure, thehead-supporting body 6 has a wide upper portion 6a which is made bypressing in contact with the platen (not shown) and a narrow lowerportion 6b. Therefore, the head-supporting body 6 according to thepresent embodiment is substantially T-shaped in the plan view.

On the other hand, the frame 12 has left and right side walls 13 and 14which are provided facing each other at a distance depending on thewidth of a recording medium (not shown). The right side wall 14 has athin portion 12a to be engaged with the wide upper portion 6a of thehead-supporting body 6 and a thick portion 12b to be engaged with thenarrow lower portion 6b of the head-supporting body 6. A substantiallyarc-like guide slit 14a is formed in the thin portion 12a while avertical guide slit 14b is formed in the thick portion 12b. In the samemanner, the left side wall 13 is divided into the thin portion 12a andthe thick portion 12b. The thin portion 12a has a substantially arc-likeguide slit 13a while the thick portion 12b has a vertical guide slit.

The distance between the two thin portions 12a which face each otheracross the width direction is set so as to exactly fit the width of thewide upper portion 6a of the head-supporting body 6. In the same manner,the distance between the two thick portions 12b which face each otheracross the width is set so as to fit the width of the narrow lowerportion 6b of the head-supporting body 6. Thus, it is possible toprovide a step between the thin portion 12a and the thick portion 12b orthe side of the frame 12 according to the difference in size of the wideupper portion 6a and the narrow lower portion 6b on the side of thehead-supporting body 6. With such a structure, the mechanical strengthof the pair of left and right side walls 13 and 14 can be improved.Since the thick portion 12b is provided utilizing the dead space insidethe frame 12, the width of the frame does not increase compared to aconventional one. The frame 12 having such a structure can be formed byinjection molding of resin or the like.

The printhead 2 is incorporated in the frame 12 dropwise from the above.By this, the printhead 2 is provided to bridge between the left andright side walls 13 and 14 of the frame 12. Looking at the right sidewall 14, the upper pin 7a of the printhead 2 is engaged with thearc-like guide slit 14a while the lower pin 7b is engaged with thevertical guide slit 14b. With respect to the left side wall 13, the samething can be said. With such a structure, the printhead 2, whilebridging across the frame 12, rotates backward and forward with thelower pin 7b being the center of the rotation. It should be noted that apredetermined clearance is left between the pin 7b and the verticalguide slit 14b so that the printhead 2 can move backward and forward alittle. When the printhead 2 rotates backward and forward, the upper pin7a moves along the arc-like guide slit 14a. Even when the printhead 2rotates forward and touches the platen (not shown), the pin 7a does nottouch the deepest portion of the guide slit 14a so that the printhead 2can tilt right and left. It should be noted that the guide slit 14aprecisely aligns the printhead 2 with respect to the vertical direction.With such a structure, the printhead 2 can tilt and displace inforward/backward and rightward/leftward directions according to theposition of the platen. On the other hand, as described above, thepressing body (not shown) is in point contact with the printhead 2.Thus, during a printing operation, the printhead 2 can be presseduniformly into contact with the cylindrical surface of the platen sothat it follows the rotation of the platen. In other words, thedimension error and the installation error of the platen can beabsorbed, and the deviation and the like can be effectively prevented.

FIG. 3A is a plan view and FIG. 3B is a right elevational view showingan example of a specific structure of a printer according to the presentinvention. This printer is basically embodied by the combination of thestructure of the pressing body shown in FIG. 1(A) and the structures ofthe printhead and the frame shown in FIGS. 2A and 2B. Therefore, likereference numerals designate corresponding parts so as to be understoodeasily. As shown in the figure, this printer is fabricated using theframe 12. The frame 12 has left and right side walls 13 and 14 which areat a distance depending on the width of a recording medium. The platen 1is rotatably provided to bridge between the two side walls 13 and 14. Asdescribed above, the platen 1 has the cylindrical elastic body 4 made ofrubber or the like and a rotating shaft 5. The rotating shaft 5 issupported by the left and right side walls 13 and 14, and is driven torotate via a motor and a series of gears (not shown). By thisconstruction, a recording medium is fed. The printhead 2 is alsoprovided to bridge between the two side walls 13 and 14, and is disposedat the back of the platen 1. As described above, the printhead 2 has thehead-supporting body 6 to the front face of which a board 15 isattached. On the board 15, a thermal element and a driving circuit aremounted. Further, a pressing member 16 of a flexible connector to beconnected with the board 15 is also attached to the front face of thehead-supporting body 6. On the other hand, the convex spherical surfaceportion 11 is formed at the back of the head-supporting body 6. Asdescribed above, the head-supporting body 6 is divided into the wideupper portion 6a and the narrow lower portion 6b. The pin 7a formed inthe wide upper portion 6a is engaged with the arc-like guide slit 14aformed in the thin portion 12a of the side wall 14. The pin 7b formed inthe narrow lower portion 6b of the head-supporting body 6 is engagedwith the vertical guide slit formed in the thick portion 12b of the sidewall 14.

The pressing body 3 has the horizontal shaft 8, by which the pressingbody 3 is incorporated in the frame 12. The torsion spring 9 whichgenerates a predetermined pressing force is wound on the horizontalshaft 8. The plane member 10 is attached to the horizontal shaft 8. Theplane member 10 is in point contact with the convex spherical surfaceportion 11 of the head-supporting body 6 described above. By thisconstruction, the pressing body 3 presses a front surface of theprinthead 2 from the rear thereof into contact with the platen 1. Theright elevational view in FIG. 3B shows the state of the contact bypressing. The thermal element mounted on the front face of thehead-supporting body 6 is in close contact with the cylindrical elasticbody 4 of the platen 1 and performs a predetermined print operation to arecording medium disposed therebetween. Here, the upper pin 7a of theprinthead 2 can move in the arc-like guide slit 14a, and thus, theprinthead 2 can tilt right and left to absorb a deviation with theplaten 1. Further, the lower pin 7b of the head-supporting body 6 isengaged wit the side wall 14 with a little clearance being left, andthus the head-supporting body 6 can tilt and move backward and forward.Thus the fine control of the tilted position of the printhead 2 withrespect to the platen 1 is possible. In other words, the positioning ofthe printhead 2 is regulated by the upper pin 7a only in the verticaldirection, and the incorporation is such that the printhead 2 can moveright and left and backward and forward with respect to the frame 12.

FIGS. 4A and 4B show only the main components of the printer shown inFIGS. 3A-3B to clarify the relation of the arrangement. As shown in thefigure, the pressing body 3 presses the printhead 2 into contact withthe platen 1. The printhead 2 is attached to the frame by a pair ofupper and lower pins 7a and 7b so as to move backward and forward andright and left. The convex spherical surface portion 11 of the printhead2 is in point contact with the plane portion 10 of the pressing body 3.With such a structure, the printhead 2 is pressed into contact with theplaten 1 following up the platen 1 in backward and forward and right andleft direction.

FIGS. 5A and 5B show an example of a variation of the structure shown inFIGS. 4A and 4B. Like reference numerals designate corresponding partsso as to be understood easily. It should be noted that this variationcorresponds to the structure shown in FIG. 1(B). The convex cylindricalsurface portion 11a which extends in the vertical direction is formed atthe back of the printhead 2. On the other hand, the middle portion 10aof the torsion spring 9 incorporated in the pressing body 3 extends inthe horizontal direction. The cylindrical surface portion of the middleportion 10a is orthogonal to and is in point contact with thecylindrical surface portion 11a on the side of the printhead 2.

FIGS. 6A and 6B show another variation of the structure shown in FIGS.4A and 4B. Like reference numerals designate corresponding parts so asto be understood easily. In the present example, the convex cylindricalsurface portion 11b in the horizontal direction is formed at the back ofthe printhead 2. On the other hand, the vertical convex cylindricalsurface portion 10b is formed in the middle of the plane member 10 ofthe pressing body 3. The convex cylindrical surface portions 10b and 11bwhich are orthogonal to each other are in point contact with each otherto enable the printhead 2 to tilt and move backward and forward andright and left.

Industrial Utilization

According to the present invention, since the operating portion of thepress is a point, a printhead can tilt and move backward and forward andright and left, and can be pressed uniformly into contact with a platen.Therefore, it is effective for improving the print quality and thelinearity of advance of a recording medium. Further, since a pressingbody and a printhead are independent of each other, a printhead can beremoved (exchanged) with ease. Still further, by making a printhead tobe T-shaped, the dead space in a frame is effectively utilized, and atthe same time, fabrication by dropping a printhead from the above ismade possible. Together with this, a thin portion and a thick portionare provided in a side wall of a frame so as to improve the strength ofthe frame.

I claim:
 1. A printer comprising: a frame having side walls spaced aparta given distance according to a given width size of a recording medium;a platen rotatably supported between the side walls; a printheaddisposed between the side walls and behind the platen, the printheadextending substantially from one side wall to the other side wall theprinthead being operable in a printing position thereof to perform aprinting operation on the recording medium; means supporting theprinthead to the side walls of the frame for movement of the printheadin forward/backward and rightward/leftward directions relative to theframe; and a pressing body supported by the frame for pressing a rearsurface portion of the printhead in point contact therewith to bring afront surface of the printhead into contact with a contacting surface ofthe platen; whereby the printhead can move in forward/backward andrightward/leftward directions relative to the frame following thecontacting surface of the platen upon movement of the printhead to theprinting position.
 2. A printer according to claim 1; wherein theprinthead and the pressing body are formed of independent componentswhich can be independently incorporated into the printer.
 3. A printeraccording to claim 1; wherein one of the printhead and the pressing bodyhas a convex spherical surface portion and the other of the printheadand the pressing body has a plane portion, the convex spherical surfaceportion and the plane surface portion being in point contact with eachother when the printhead is in the printing position.
 4. A printeraccording to claim 1; wherein the printhead and the pressing body haveconvex cylindrical surface portions which intersect each other and arein point contact with each other when the printhead is in the printingposition.
 5. A printer according to claim 1; wherein the printhead has awide upper portion and a narrow lower portion integral with the wideupper portion, the wide upper portion having the front surface of theprinthead which is pressed into contact with the contacting portion ofthe platen when the printhead is in the printing position; and whereinthe side walls have thin portions for engagement with the wide upperportion of the printhead and thick portions for engagement with thenarrow lower portion of the printhead.
 6. A printer according to claim1; wherein the pressing body comprises a biasing member.
 7. A printeraccording to claim 6; wherein the biasing member comprises a torsionspring having a horizontal portion centrally thereof for pressing therear surface portion of the printhead in point contact therewith.
 8. Aprinter according to claim 6; wherein the biasing member comprises ashaft rotatably supported by the frame, a plane portion integrallyconnected to the shaft centrally thereof, and a torsion spring forpressing the plane portion into point contact with the rear surfaceportion of the printhead.
 9. A printer according to claim 6; wherein thebiasing member comprises a first shaft rotatably supported by the frame,a second shaft integrally connected to the first shaft centrallythereof, and a torsion spring for pressing the second shaft into pointcontact with the rear surface portion of printhead.
 10. A printeraccording to claim 9; wherein each of the rear surface portion of theprinthead and the second shaft of the biasing member has a convexcylindrical surface in point contact with each other when the printheadis in the printing position.
 11. A printer according to claim 1; whereinthe printhead comprises a support body; and wherein the means supportingthe printhead comprises a pair of pins extending from the support bodyeach for engagement with one of the side walls of the frame.
 12. Aprinter according to claim 1; wherein the printhead comprises a supportbody having a first portion and a second portion integral with the firstportion; and wherein the means supporting the printhead comprises afirst pair of pins extending from the first portion each for engagementwith one of the side walls of the frame, and a second pair of pinsextending from the second portion each for engagement with one of theside walls of the frame.
 13. A printer comprising: a frame having leftand right side walls spaced apart a given distance according to a givenwidth size of a recording medium, the side walls having first portionshaving a first preselected thickness and second portions having a secondpreselected thickness greater than the first preselected thickness; aplaten rotatably supported between the side walls; a printhead rotatablysupported between the side walls and disposed behind the platen, theprinthead having an upper portion supported by the first portions of theside walls and a lower portion integral with the upper portion andsupported by the second portions of the side walls, the upper portionhaving a first preselected width, the lower portion having a secondpreselected width smaller than the first preselected width, and theupper portion having a contact surface which is pressed into contactwith the platen; and a pressing body for pressing the contact surface ofthe upper portion of the printhead from a rear portion thereof intocontact with the platen.
 14. A printer comprising: a frame having a pairof side walls spaced apart a given distance according to a given widthsize of a recording medium; a platen supported between the pair of sidewalls and having a surface for supporting the recording medium; aprinthead supported between the side walls and operable in a printingposition thereof to perform a printing operation on the recordingmedium; the printhead extending substantially from one side wall to theother side wall and support means for supporting the printhead formovement in forward/backward and rightward/leftward directions relativeto the frame, following the surface of the platen, when the printhead isin the printing position.
 15. A printer according to claim 14; whereinthe support means comprises support members for pivotally supporting theprinthead to the frame, and a pressing body for pressing a rear surfaceportion of the printhead in point contact therewith to bring a frontsurface of the printhead into contact with the surface of the platen.16. A printer according to claim 15, wherein the printhead comprises asupport body; and wherein the support members comprise a pair of pinsextending from the support body each for engagement with one of the sidewalls of the frame.
 17. A printer according to claim 15; wherein theprinthead comprises a support body having a first portion and a secondportion integral with the first portion; and wherein the support memberscomprise a first pair of pins extending from the first portion each forengagement with one of the side walls of the frame, and a second pair ofpins extending from the second portion each for engagement with one ofthe side walls of the frame.
 18. A printer according to claim 15;wherein one of the printhead and the pressing body has a convexspherical surface portion and the other of the printhead and thepressing body has a plane surface portion in point contact with theconvex spherical surface portion.
 19. A printer according to claim 15;wherein each of the printhead and the pressing body has a convexcylindrical surface portion in point contact with each other when theprinthead is in the printing position.
 20. A printer according to claim15; wherein the pressing body comprises a biasing member.
 21. A printeraccording to claim 20; wherein the biasing member comprises a torsionspring having a horizontal portion centrally thereof for pressing therear surface portion of the printhead in point contact therewith.
 22. Aprinter according to claim 20; wherein the biasing member comprises ashaft rotatably supported by the frame, a plane portion integrallyconnected to the shaft centrally thereof, and a torsion spring forpressing the plane portion into point contact with the rear surfaceportion of the printhead.
 23. A printer according to claim 20; whereinthe biasing member comprises a first shaft rotatably supported by theframe, a second shaft integrally connected to the first shaft centrallythereof, and a torsion spring for pressing the second shaft into pointcontact with the rear surface portion of printhead.
 24. A printeraccording to claim 23; wherein each of the rear surface portion of theprinthead and the second shaft of the biasing member has a convexcylindrical surface in point contact with each other when the printheadis in the printing position.
 25. A printer according to claim 14;wherein each of the side walls has first portions having a firstpreselected thickness and second portions having a second preselectedthickness greater than the first preselected thickness; and wherein theprinthead has an upper portion supported by the first portions of theside walls and a lower portion integral with the upper portion andsupported by the second portions of the side walls, the upper portionhaving a first preselected width, the lower portion having a secondpreselected width smaller than the first preselected width.
 26. Aprinter comprising: a frame having a pair of side walls spaced apart agiven distance according to a given width size of a recording medium; aplaten supported between the pair of side walls and having a surface forsupporting the recording medium; a printhead supported between the sidewalls and operable in a printing position thereof to perform a printingoperation on the recording medium; the printhead extending substantiallyfrom one side wall to the other side wall means supporting the printheadto the side walls of the frame for movement of the printhead inforward/backward and rightward/leftward directions relative to theframe; and a pressing body supported by the frame for pressing theprinthead into contact with the surface of the platen; whereby theprinthead can in forward/backward and rightward/leftward directionsrelative to the frame to permit angular adjustment thereof, followingthe surface of the platen, when the printhead is in the printingposition.
 27. A printer according to claim 26; wherein the pressing bodypresses the printhead in point contact therewith when the printhead isin the printing position.
 28. A printer according to claim 26; whereinthe printhead comprises a support body; and wherein the means supportingthe printhead comprises a pair of pins extending from the support bodyeach for engagement with one of the side walls of the frame.
 29. Aprinter according to claim 26; wherein the printhead comprises a supportbody having a first portion and a second portion integral with the firstportion; and wherein the means supporting the printhead comprises afirst pair of pins extending from the first portion each for engagementwith one of the side walls of the frame, and a second pair of pinsextending from the second portion each for engagement with one of theside walls of the frame.